Solid state energy storage device

ABSTRACT

A disc of sintered zirconium oxide and yttrium oxide is sandwiched between electronically and anionically conductive discs of cerium oxide. The intermediate disc consists of an electronically insulative structural lattice that contains oxygen anions capable of migrating in relationship to said lattice under the influence of an external electric field. At temperatures of about 500*-1500* C. and under the influence of such an electric field, oxygen anions travel from one side disc through the intermediate disc to the other side disc while the corresponding electrons travel through an external circuit.

United States Patent [72] Inventors Joseph T. Kummer [56] ReferencesCited g Ann Am bom Mi h UNITED STATES PATENTS seng en, r, o c [211 App].No 877,348 3,499,796 3/ 1970 Hever et al. 136/83 [22] Filed Nov. 17,1969 Primary Examiner-Winston A. Douglas [45] Patented Sept. 21, 1971Assistant Examiner-A. Skapars [73] Assignee Ford Motor CompanyAttorneys-John R. Faulkner and Glenn S. Arendsen Dearborn, Mich.

ABSTRACT: A disc of sintered zirconium oxide and yttrium oxide issandwiched between electronically and anionically [54] g i g EgERGYSTORAGE DEVICE conductive discs of cerium oxide. The intermediate disccon- 6 Ch sists of an electronically insulative structural lattice thatcon- [52] U.S.Cl 136/83, tains oxygen anions capable of migrating inrelationship to 136/ 153, 317/258 1 said lattice under the influence ofan external electric field. At [51] Int. Cl ..H01m 21/00, temperaturesof about 500-1500 C. and under the influence HOlg 1/00 of such anelectric field, oxygen anions travel from one side [50] Field 01 Search136/83, 86, disc through the intermediate disc to the other side discwhile the corresponding electrons travel through an external circuit.

PATENTED SEFZI nan F/G J JAM ATTORNEYS SOLID STATE ENERGY STORAGE DEVICESUMMARY OF THE INVENTION This application relates to US. Pat.application by I-Iever et al. Ser. No. 595,814, now US. Pat. No.3,499,796 filed Nov. 21, 1966 and assigned to the assignee of thisapplication. The

entire disclosure of application Ser. No. 595,814 is incorporated hereinby this reference.

The Hever et al. application provides a solid state energy storagedevice in which an electrical field produces cations in one side memberthat migrate through a cationically conductive but electronicallyinsulative intermediate member to another side member. Electrons givenup by the cations travel through an external circuit connected to theside members. When the electrical field is removed, the cations returnto the original side member through the intermediate member while theelectrons return to the original side member through the externalcircuit.

This invention provides a solid state energy storage device in which anelectrical field produces anions in one side member that migrate throughan electronically insulative intermediate member to the other sidemember. The device comprises a ceramic sandwich having two side membersin anion exchange relationship with and separated by an intermediatemember. Each of the side members consists essentially of apolycrystalline material comprising an electronically conductivestructural lattice containing anions that migrate relative to thelattice. Ions of a metal in two valence states and ions of oxygenpreferably make up the lattice. The intermediate member consistsessentially of an electronically insulative structural latticecontaining oxygen anions that migrate in relation to said lattice underthe influence of an electric field.

Heating the device to a temperature of at least about 500 C. andapplying an electrical field thereto moves oxygen anions from one sidemember to the other side member through the intermediate member. Goodoperations can be obtained at temperatures ranging up to about 1,500 C.although the device is most economical in the 5001,000 C. range.Electrons surrendered by the anions move through an external electricalcircuit connecting the side members. When the field is removed, theanions return to the original side member through the intermediatemember and the electrons return to the original side member through theexternal circuit, thereby producing an electrical current in theexternal circuit. Thus the device is capable of acting as a solid statecapacitor or energy storage device.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional view of adevice of this invention showing the side and intermediate layers.Conductors are attached to the side layers for connection to an externalcircuit.

DETAILED DESCRIPTION Referring to the drawing, side members 1 and 2 areelectronically and anionically conductive materials. The side memberstypically are crystalline materials formed from a carefully selectedsintered mixture of ceric oxide and cerous oxide. Mixture ingredientsare selected to give a resulting cerium oxide composition having a molarratio of oxygen to cerium numerically between the molar ratios of theelements in the two valencestates of cerium. Good results are obtainedwith molar ratios between about 1.80 and 1.99 with best results beingprovided by a preferred range of 1.90 to 1.95.

An anionically conductive, electronically resistive ceramic member 3 issandwiched between side members 1 and 2. Intermediate member 3 typicallyconsists essentially of a solid solution 'of zirconium oxide and yttriumoxide or zirconium oxide and calcium oxide. The mixture generallycontains about 80-95 mole percent zirconium oxide with the balanceyttrium oxide or calcium oxide. Best results are obtained with about88-92 mole percent zirconium oxide.

Members 1, 2 and 3 are assembled together and sintered in a hot pressingoperation at about 1,300 C. The hot pressing operation typically iscarried out above 5,000 p.s.i. and preferably is conducted at pressuresof about 50 p.s.i. to 10,000 p.s.i. This compressing and sinteringoperation produces a good anion exchange relationship between each sidemember and the intermediate member.

Metal conductors 4 and 5 are attached electrically to the externalsurfaces of members 1 and 2. Useful conductors are platinum sheets orfoils. Conductor leads 6 and 7 then are attached to conductors 4 and 5and connected to an external electrical circuit (not shown).

When an electrical energy source included in the external circuitapplies an electrical potential across conductors 4 and 5, electrom arepumped from the side member connected to the positive terminal of theenergy source to the side member connected to the negative terminal.Oxygen anions pass from the side member connected to the negativeterminal through the intermediate member to the other side member.Removing the electrical potential permits the flows to reverse and thusproduces an electric current in the external circuit.

EXAMPLE Powders of chemically pure zirconium oxide and yttrium oxide aremixed together thoroughly in acetone, dried and sintered at about 1,350C. for 24 hours in a platinum container. The reaction product is ground,pressed into a disc at about 40,000 p.s.i. and sintered at l,8002,000 C.in an inert atmosphere.

End members are prepared by mixing powdered ceric oxide and cerous oxidein proportions selected to provide an overall composition having a molarratio of oxygen to cerium between 1.90 and 1.95 After thorough mixing,the I powders are pressed at about 40,000 p.s.i. into discs and sinteredat 1,800-2,000 C. in an inert atmosphere.

Two of the cerium oxide discs are placed on opposite sides of thezirconium oxide-yttrium oxide disc and a sheet of 0.0005 inch thickplatinum foil is placed on each exterior surface of the cerium oxidediscs. The resulting sandwich is hot pressed at 1,300 C. and 5,000p.s.i. for about 1 hour to produce a unitary structure. Hot pressingproduces an excellent anion exchange relationship between the endmembers and the intermediate member and between the platinum foils andthe end members.

When the device is assembled to an external electrical circuit thatapplies an electrical potential thereto and its temperature is raised toabout 500-1,5000 C., anions of oxygen migrate through the intermediatemember while the electrons corresponding thereto migrate through theexternal circuit. When the external circuit is interrupted and theelectrical field is removed, the unbalanced situation existing withinthe device produces an electrical potential across its terminals. Whenthe external circuit is reconnected, anions return to the original sidemember through the intermediate member and electrons flow through theexternal circuit to link up with the returning anions.

Thus the device serves as an energy storage device such as a capacitoror battery. The device is particularly useful in conjunction with fuelcells that operate at elevated temperatures where the device can be usedto store energy to meet temporary demands in excess of the ratedcapacity of the fuel cell.

We claim:

1. A solid state energy storage device comprising a ceramic sandwichhaving two end members in anion exchange relationship with and separatedby an intermediate member, each of said end members consistingessentially of a polycrystalline material comprising an electronicallyconductive structural lattice containing anions that migrate relative tosaid lattice, said lattice comprising ions of oxygen and ions of a metalin two valence states, said intermediate member consisting essentiallyof an electronically insulative structural lattice containing anionsthat migrate in relation to said lattice under the 4. The energy storagedevice of claim 3 in which the molar ratio of oxygen ions to cerium ionsis about l.90l .95.

5. The energy storage device of claim 4 in which the intermediate membercomprises a solid solution of zirconium oxide and yttrium oxide orzirconium oxide and calcium oxide.

6. The energy storage device of claim 1 in which the intermediate membercomprises a solid solution of zirconium oxide and yttrium oxide orzirconium oxide and calcium oxide.

2. The energy storage device of claim 1 in which said anions are oxygenions.
 3. The energy storage device of claim 2 in which the metal havingtwo valence states is cerium and the molar ratio of the oxygen ions tothe cerium ions is between the molar ratios at said two valence states.4. The energy storage device of claim 3 in which the molar ratio ofoxygen ions to cerium ions is about 1.90-1.95.
 5. The energy storagedevice of claim 4 in which the intermediate member comprises a solidsolution of zirconium oxide and yttrium oxide or zirconium oxide andcalcium oxide.
 6. The energy storage device of claim 1 in which theintermediate member comprises a solid solution of zirconium oxide andyttrium oxide or zirconium oxide and calcium oxide.